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BQ40Z80: AOLD trip before threshold

Peyton
Prodigy 50 points
Part Number: BQ40Z80

Hello TI Team,

We have a BQ40Z80 in use with a 3S LiPo battery used in a drone. Currently the AOLD threshold is set to 0xFF, and RSNS is set to 1. We have a 3mOhm sense resistor. With these settings and sense resistor we expect to see AOLD trip at 33.33A. During testing we are seeing AOLD trip at 27.6A while being tested on a DC load, and during flight conditions we can trigger AOLD with an aggressive throttle response and rapid transients.  

Swapping the sense resistor to 1mOhm fixes our issue,  but we are wondering if there is any insight for why rapid current spikes under the threshold would trip the AOLD protections? 

Best,
Peyton

  • 0
    TI__Guru** 105770 points

    Hello Peyton,

    The hardware current protections accuracy range is fairly wide due to the thresholds essentially modifying the trim values in the gauge hardware. That being said I think the ~6A difference between the programmed and real protection trip point is a little high. Can you share any scope captures of the bench tests so we can see the exact timing and amplitude of the failure? Can you also share your .gg file with the settings?

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 50 points

    Hello, I don't have captures from these tests. What would the accuracy range be? We saw different behavior among our batch of 18 batteries. Most cut out between 29-31A with the AOLD protection set to be 33.33A. Only a few tripped at the 27.6A value.

    When I receive more batteries I can rerun the tests before swapping out the resistor and report back, although I am fairly confident the wider range is the culprit.

    Best,
    Peyton

  • +1 in reply to Peyton
    TI__Guru** 105770 points

    Hello Peyton,

    The threshold accuracy is in the datasheet on page 13, the error should be up to 10% with no trim. So 29A would be the worst case error we would expect.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 50 points

    Thank you, with this in mind and a new sense resistor of 1mOhm, we have seen no more issues.